Come to think of it, I've never had a hard drive fail either. This would be my 4th computer.
It's too early to say if the USB drive will fail, as I've only had it 2 years or so.
But it seems that it's basically hit & miss these days, as the quality control of many products has drastically decreased or is even non-existent.
Actually, the one internal drive that looked as though it failed and was replaced, worked fine a few weeks later as a slave in another computer!
The danger with external HDDs as I see it is that they can get bumped. My NAS drive sits on the floor behind my chair in my living room and we no longer have pets or ankle biters. Of course an SSD is immuine to shocks but the G4$ ratio is still poor and you want a back up drive to be BIG!
Dave.